Calorimetric analysis of the structural relaxation in partially hydrated amorphous polysaccharides. II. Phenomenological study of physical ageing.

Any glassy material stored at a temperature below its glass transition temperature experiences a structural relaxation that occurs as a function of time and temperature. Using Differential Scanning Calorimetry, enthalpy relaxation was studied on a series of hydrated polysaccharides in comparison with synthetic polymers, poly(methyl methacrylate) (PMMA) and poly(vinyl pyrrolidone) (PVP). The ageing kinetics were evaluated from the relaxation function based on the fictive temperature evolution. While extruded starch equilibrated apparently within the experimental time, amylopectin and phytoglycogen aged slightly faster than PMMA and hydrated PVP without reaching completely their equilibrium. Ageing effects detected after short ageing at very low temperatures (Tg−100°C) revealed the wideness of the relaxation time spectrum.